The invention relates to a cassette seal for a shaft.
A known cassette seal has a outer ring for mounting the cassette seal on a structure. A lipped sealing ring is sealingly affixed to an inward, annular projection of the outer ring for slidingly and sealingly engaging with a resilient bias about a radially-outside, axial surface of a protective sleeve. The protective sleeve is coaxially inside the outer ring for sealing about a shaft axially therethrough and rotation therewith relative to the outer ring. The protective sleeve has an outward, annular projection. A resilient protective ring, sealingly fixed to the outward projection of the protective sleeve, has a lip sealingly pressing against the inward projection of the outer ring to protect the sealing ring from foreign bodies, like dust, for example.
U.S. Pat. No. 3,682,488 describes such a cassette seal. The lip of its protective ring extends axially to contact a countersurface on the inward projection of the outer ring which extends radially. The effectiveness of this arrangement depends on precise association of the parts of the seal with one another. Complex adjusting work during assembly is, therefore, unavoidable.
Even this does little good, however, if relative displacement in the axial direction occurs between the lip of the protective ring and its countersurface during normal operation, or if wear occurs in this critical area. Both do.
Inasmuch as the protective ring is fixed to the protective sleeve which is fixed to the shaft and the countersurface for its lip is on the outer ring which mounts the cassette seal, axial displacement of the shaft in normal, rotational operation produces such relative axial displacement between the lip of the protective ring and its countersurface. Inasmuch as the lip of the protective ring slides on its countersurface when these relatively rotate with the shaft and outer ring, these always wear in time.